Both ITK (python package) and SimpleITK (python package) are bindings of ITK C++ library providing a number of verified utilities for medical image processing, especially 3D volumetric image processing.
ITK python package provides both C++ style bindings ( functions and classes in UpperCamelCase ) and pythonic bindings ( in snake_case ). C++ style bindings keeps the original pipeline structure and template programming style in ITK and the pythoic bindings provides somewhat procedural interface. For example, in C++ style bindings, you need to specify the datatype when instantiating filters, an example is as following. Refer to the tutorial for more information.
InputType = itk.Image[itk.F,3]
OutputType = itk.Image[itk.F,3]